- A crystal structure is formed by arranging basis groups of atoms in a periodic three-dimensional lattice. The smallest repeating unit of a crystal structure is the unit cell. - Key parameters that define a crystal structure include the lattice type, basis, unit cell dimensions and angles, crystal system, and Miller indices of lattice planes. - Common crystal structures include simple cubic, body-centered cubic, face-centered cubic, and hexagonal close-packed. Polymorphism and allotropy refer to a material having more than one possible crystal structure.

2. Lattice
• Regular , periodical arrangements of points in
three dimension.
• Lattice point : The points which presents in
the lattice

3. Basis
• Group of atom is called as basis

4. Crystal structure
• Lattice + basis = crystal structure
• Crystal structure is obtained by arranging the
basis in each and every lattice point

5. Unit cell
• Smallest geometric figure , by the repetition of
this we get complete crystal structure.

6. Crystal parameters
• The three mutual perpendicular lines OX,OY
and OZ.
• Inter axial lengths: OA = a , OB = b and OC = c
• Inter axial angles: α,β and γ

7. Crystal system
Cubic
Orthorhombic
Monoclinic
Triclinic
Hexagonal
Rhombohedral
Tetragonal

9. Bravais lattice

10. Lattice planes

11. Miller indices

12. d spacing in cubic lattice
a
d
h2 k2 l2

13. Calculation of number of atoms
per unit cell – Atomic radius –
Coordination number – Packing
factor for SC , BCC ,FCC and HCP

14. Simple Cubic structure

15. Atomic radius(r)
• r = a/2

16. Coordination number (N)

17. Body Centered Cubic

18. Number of atoms per unit cell

19. Coordination number
• For BCC the coordination number is 8

20. Face Centered Cubic

21. • Atomic radius = a √2 / 4

22. HCP

23. Na Cl structure

24. ZnS Structure

25. diamond and graphite Structure

27. Polymorphism and allotropy
• Polymorphism is a physical phenomenon where
a material may have more than one crystal
structure.
• A material that shows polymorphism exists in
more than one type of space lattice in the solid
state. If the change in structure is
reversible, then the polymorphic change is
known as allotropy.
• The prevailing crystal structure depends on both
the temperature and the external pressure.

28. • Allotropes of carbon
Diamond and graphite

29. Crystal defects
• Point defect
• line defect
• surface defect
• Burger vector

30. Point defect

31. Line defect

32. Burger vector

34. Dislocations